You can also do Star Ruby Encrusted Steins. They take more subcombines, however all the components are vender-bought (other than magic clay from a lvl 8 chanter). The cost is about 80pp per successful combine and the finished stein tributes for 234. More time intensive, but you get more out of it for your efforts besides just skill ups.

12 hours of foraging netted me 15 cosgrove powder and 15 brells bounty and a couple of stack so of water and roots. Unfortunately that is not the way to go. I tried killing Cooling Chambers for a bit but didn't even a pick up a one in 2 hours of slaying.

I maxed pottery the same way as Goofy and Sharrien... however I've been putting the cosgrove powder I've been getting in UF progression tasks in the GB.. hopefully they find their way to you. Seems I get a couple per task if I remember to loot.

I really would shy away from using cosgrove powder for skillups. Besides all it's uses in UF tradeskills it can also be transformed into chronal resonance dust which is used to make powersources among other things. All that means demand for cosgrove powder is very high and is forcing the baz price up.